Geographic variation of reproductive diapause in the Drosophila auraria complex (Diptera: Drosophilidae)

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Abstract
In the Drosophila auraria complex (D. auraria Peng, D. biauraria Bock & Wheeler, D. triauraria Bock & Wheeler, D. quadraria Bock & Wheeler and D. subauraria Kimura), D. triauraria from the island of Yaku (30.3d̀N in latitude) and D. quadraria from Taiwan (24.1d̀N) had no or weak diapause, while strains of all the four species from the main islands of Japan had a firm reproductive diapause. These strains entered diapause at short daylengths and the critical daylength was longer and the incidence of diapause higher at a low rather than high temperature. In each species, the critical daylength was longer in strains from higher latitudes. Among sympatric populations of different species, D. subauraria always had the longest critical daylength, while D. auraria had the shortest one. The populations of D. biauraria and D. triauraria had longer critical daylengths than the sympatric populations of D. auraria, but this difference became smaller northwards. Since a longer critical daylength induces diapause earlier in autumn, D. subauraria would enter diapause earliest among these species, and D. auraria would do so latest. The late start of diapause in D. auraria may be related to its adaptation to domestic environments. On the other hand, the adaptive significance of the late start of diapause in northern populations of D. biauraria and D. triauraria is not clear.